U.S. Pat. Nos. 4,220,227 and 4,502,574 disclose adjuster mechanisms for use in a drum brake to control the extension of a strut member and define a running clearance between a friction surface on brake shoes and a drum member. In particular, the adjuster mechanism includes a pawl carried by a first brake shoe wherein a spring is connected to the pawl and the other brake shoe such that movement of the first brake shoe toward the drum causes the pawl to pivot on the first brake shoe. When a predetermined movement of the brake shoe occurs as when lining wear occurs, the pawl pivots to an extent that a first edge moves past a tooth on a star wheel and when the brake application terminates, the first edge again engages the tooth and rotates the star wheel to cause an extension in the strut member. This type adjuster mechanism functions in an adequate manner for most operations, however, should the drum brake be operated under extreme conditions such as when the thermal energy generated during a brake application caused the drum to expand and now when an input force is applied to moves the friction surface on the brake shoe into engagement with the drum it is possible that the first edge on the pawl will move past several teeth on the star wheel. Now on return of the pawl to a rest position, a second edge engages the star wheel and rotates the star wheel through an arc corresponding to several teeth such that a desired running clearance is largely reduced or non-existent. Thereafter when the drum cools, it contracts and if the running clearance is totally eliminated, the brake will drag until the friction lining is worn away through continued engagement with the drum. Thus, it is important to control the rotation of the star wheel so that the extendable strut is not over adjusted and the brake shoes are maintained with a desired running clearance with respect to the drum.
In order to prevent such over adjustment caused by thermal expansion, a bimetallic member has been placed in the expandable strut as disclosed in U.S. Pat. No. 4,390,086 and on an end member to engage the pawl as disclosed in U.S. Pat. No. 6,691,838 and a leg of the pawl as disclosed in U.S. Pat. No. 4,385,681 to move the pawl out of engagement with the star wheel when a predetermined temperature is generated during a brake application. While brakes having such bimetallic members function in an adequate manner it has been observed that under some conditions, over adjustment may still occur as the thermal energy generated during a brake application is not directly conducted into the bimetallic strip but passes though several members and as a result a delay occurs in the disengagement of the pawl and the star wheel.